Clocked scanning system

ABSTRACT

A clocked scanning glow discharge device wherein the rate of scan from end to end of a series of side by side glow discharge gaps between opposed electrodes in a common envelope is governed by a pair of alternating potential sources of opposite phase which add or substract to a bias potential on one of the electrodes an increment of potential sufficient to initiate or extinguish the glow discharge, capacitors for each gap being charged to effect extinguishment and prevent reversed scanning.

United States Patent Sliker 3,736,462 May 29, 1973 CLOCKED SCANNING SYSTEM Lawrence S. Sliker, Welland,

Ontario, Canada Inventor:

Assignee: International Scanning Devices, Inc.,

Fort Erie, Canada Filed: May 25, 1971 Appl. No.: 146,752

U.S. Cl. ..315/84.6, 328/211, 328/251 Int. Cl ..l-l0lj 17/48 Field of Search ..3l5/8.5, 84,5, 84.6, 315/8.6; 328/125, 210, 211, 250, 251;

References Cited UNITED STATES PATENTS 4/l95l Hough ..328/211 4/1956 Hough et al. ..328/211 X 9/1953 Lair... ..3l5/84.6 11/1958 0st ..3l5/84.6

Crowther et al ..3 l5/84.6

OTHER PUBLICATIONS Electronics pages 112-117, Vol. 43 dated May 25, 1970 Primary Examiner-Stanley D. Miller, Jr. Attorney-Scrivener Parker Scrivner and Clarke [57] ABSTRACT A clocked scanning glow discharge device wherein the rate of scan from end to end of a series of side by side glow discharge gaps between opposed electrodes in a common envelope is governed by a pair of alternating potential sources of opposite phase which add or substract to a bias potential on one of the electrodes an increment of potential sufficient to initiate or extinguish the glow discharge, capacitors for each gap being charged to effect extinguishment and prevent reversed scanning.

2 Claims, 5 Drawing Figures Envelope with Gas at pressure Patented May 29, 1973 3,736,462-

2 Sheets-$heet 1 Envelope with o o T 1520s at pressure Trigger Elecfredee Flip-Flop mvsmo LAWRENCE s suxsn M Jm w lm ATTQRNE Patented May 29, 1973 3,736,462

2 Sheets-Sheet 2 Envelope with (ice at pressure -5 1 Envelope with 72 i o 4 o c l Tran" 0 Go: of pressure Electrodes Y T T J-T .5 7 "T m T n 1%? l INVENTO LAWRENCE S- SLI KER CLOCKED SCANNING SYSTEM This application relates to scanning glow discharge tubes and more particularly to improved means for controlling the rate of scan of a glow discharge tube.

In co-pending application Ser. No. 146,753, filed May 25, 1971 and assigned to the same assignee as the present application, there is described a scanning glow discharge device comprising pairs of opposed electrodes defining a series of longitudinally aligned glow discharge gaps in a common envelope containing an ionizable medium. In the co-pending application the glow discharge is caused to move from gap to gap automatically in the direction of scan without the application of exterior power means such as a magnetic drive. This result is accomplished by providing in the circuit of each gap a capacitor with means being also provided to apply a bias potential to the common electrode sufficient to sustain glow discharge at the gaps but insufficient to initiate glow discharge except in the presence of ions and electrons in the region of the gap produced by a glow discharge in an adjacent gap. A trigger electrode at one end of the gap produces a triggering glow discharge which upon extinguishment effects the immediate production of a glow discharge in the first gap between the electrodes. This glow discharge completes the circuit to the capacitor which is then charged to a level wherein the current across the gap falls to a level insufficient to sustain the glow discharge which is thereupon extinguished and a glow discharge appears at the second gap due to the presence of ions in the immediate vicinity of that gap. The glow discharge in the second gap does not jump back to the first gap due to the continued charged condition of the capacitor, a resistance being provided in the capacitor circuit to slowly discharge the same at a rate which prevents the re-establishment of a glow discharge at the first gap until a glow discharge has been established at the third gap. Thus the glow discharge travels along the lines of the gaps in one direction only and does not skip over the next adjacent gap to some other downstream gap' because of the rapid fall off of the ionization of the medium short of succeeding gaps beyond the next adjacent gap.

Though the arrangement of the co'pending application works effectively, because of variations in capacitor construction and other variables there is sometimes a variation in the rate at which successive capacitors are charged to a level effecting extinguishment of a glow discharge and thus the rate of scan may be subject to undesirable variations.

The object of the present invention is to precisely control the rate of scan by superimposing on the charge received by each capacitor from the bias potential a pulse derived from one of a pair of pulsating transfer voltage signal sources of opposite phase one each of said sources being connected in common to alternate capacitors with the sources being adapted to apply to said capacitors in alternate, clocked phase relationship a momentary increase or decrease of potential to effect extinguishment or initiation of a glow discharge at each successive gap. Stated differently, instead of the rate of scan being dependent on the characteristics of the capacitors, the rate is dependent entirely upon the characteristics of the voltage transfer signal sources.

It is known in the art that electrodes in glow discharge devices are subject to deterioration due to sputtering which is generally defined as the transfer of metal from one electrode to the other as the result of the propagation of a glow discharge between the electrodes. A subsidiary object of the present invention is to eliminate to a substantial degree the transfer of metal from one electrode to another clue to sputtering by providing means for alternating the polarity of the bias potential on each successive scan. It has been found that such an arrangement prolongs the life of a glow discharge device far beyond what has been possible with systems where the polarity of the glow discharge device is always the same.

Referring now to the drawings wherein:

FIG. 1 illustrates the current versus voltage operating characteristics of two adjacent pairs of electrodes in a common envelope;

FIG. 2 is an electrical schematic diagram of a glow discharge system incorporating the present invention;

FIG. 3 illustrates the current versus voltage operating characteristic at one gap of a glow discharge device;

FIG. 4 is an electrical schematic diagram of a second embodiment of a glow discharge device constructed in accordance with the invention and wherein the polarity is reversed on successive scans; and

FIG. 5 is an electrical schematic diagram of a third embodiment of a glow discharge device incorporating the present invention.

Referring now to FIG. 1, as already described in our co-pending application, when a glow discharge is first established a current L, is established at the gap sufficient to sustain the glow. With a capacitor in series with the gap, as the capacitor charges the current at the gap falls to a level I, where the glow is extinguished. With the potential at the next adjacent gap being sufficient to sustain a glow discharge but insufficient to initiate discharge except in the presence of ions and electrons resulting from the glow discharge in the first gap, when these are received at the second gap a glow discharge is established there, with the current at the gap being again decreased by charging of the second capacitor until the glow in the second gap is extinguished.

Referring now to FIG. 2, the numeral 10 refers to a scanning tube envelope containing a pressurized ionizable medium and a first electrode means represented by an elongated common electrode 12 which is adapted to be connected to a source of bias potential by way of a lead 14. Spaced in opposition to the electrodes 12 are a series of side by side sets of alternate individual electrodes 16, 18 spaced from the electrode 14 to define between them a line of glow discharge gaps 19.

Each alternate electrode 16 of one set is connected through a capacitor 21, bridged by a resistor 22, to a common transfer line 23 and each electrode 18 of the other set of alternate electrodes is connected through a capacitor 24, also bridged by a resistor 22, to a second, common transfer line 26. The respective transfer lines 23, 26 are connected to sources 28, 30 of alternating potential of opposite phases whose outputs, upon the application of bias potential to the common elec' trode 12, are algebraically added thereto in phased relationship to initiate and extinguish glow discharge in the gap 19 as hereinafter described.

Operation of the scanner tube of FIG. 2 commences by the delivery to the trigger electrodes 20 of a high voltage pulse sufficient to establish a glow discharge between the trigger electrodes.

Simultaneously, a bias voltage V is applied to the common electrode 12 and when this potential is added to the peak potential supplied during one half cycle of the source 28 connected to transfer line 23, the combined potential is sufficient to sustain a glow discharge in the first gap 19 between the common electrode 12 and the first electrode 16. The combined potential is selected so as to be insufficient to initiate glow discharge except in the presence of ions and electrons resulting from the glow discharge of the trigger gap. When the trigger glow is extinguished, a glow discharge appears at the first gap and is sustained until the first capacitor 21 is charged by the bias potential to a level which is insufficient by itself to lower gap current to the point of extinguishing the glow discharge at the first gap. However, when the peak of the next half cycle of the source 28 is reached, a sufficient charge is then placed on the capacitor 21 to effect extinguishment of the glow discharge in the first gap.

Meanwhile, the second source 30 provides during its first half cycle, a peak potential enabling a glow discharge at the second gap when ions and electrons resulting from the first glow discharge are received in the region of the second gap. in the next half cycle of the source 30 the charge on the second capacitor 24 is raised to a level where the current at the second gap is no longer sufficient to sustain the glow discharge at that gap and the glow is extinguished with the third gap being enabled as described for the first two gaps. Thus the scanning tube is scanned from one end to the other and at the last gap a second pulse can be supplied to the trigger electrode to commence a second cycle or, if desired, the bias potential can be lowered to deactivate the tube.

After a glow discharge is extinguished at, say, the second gap, it will be re-established at the third gap rather than at the first because the resistor 22 bridging the first capacitor is selected to retain sufficient charge on the capacitor to prevent the re-establishment of a glow at the first gap. The rate of capacitor discharge afforded by the resistor 22 is selected to retain sufficient charge on the capacitor until after the glow discharge has been established at the third gap in the line of scan. At this gap the distance is too great for the locally ionized medium to have any effect except on the immediate adjacent gap downstream, the one upstream having been disabled by its capacitor as just explained.

With reference again to FIG. 1 and also to FIG. 3 the bias potential is represented by the line V The additional potential V, required to initiate the glow discharge in the presence of ions is derived by combining the potentials from the appropriate half cycle of either the source 28 or 30 with the bias potential. This combined potential is sufficient to sustain glow discharge but during the second half cycle of the appropriate source, the capacitor is charged to a level which immediately shifts the load line R to a point where the glow discharge can no longer be sustained.

A glow discharge between electrodes is known to produce sputtering whereby metal from one electrode is deposited on the other. This causes early deterioration of the electrodes and in accordance with the present invention the effects of sputtering can be largely eliminated by reversing the polarity of the bias potential on each successive scan. An arrangement for accomplishing this is shown in FIG. 4.

As with FIG. 1, an envelope 30 containing an ionizable medium encloses a common electrode 32 and a plurality of side by side electrodes 34, 36 arranged in alternate sets. Each electrode 34, 36 of the respective sets is connected through a capacitor 38 to a respective transfer line 40, 42 connected to alternating potential sources 44, 46 of opposite phases, these being in the branched terminal lines of a source of bias potential whose other terminal is connected to the common electrode 32. The bias terminals are connected through a switching amplifier 48 or other known pulse responsive switch means to either a source of negative potential 50 or a source of positive potential 52.

The amplifier is switched to connect the terminals to either the positive or negative polarity sources in response to a trigger input as shown at 56 whose prime function is to initiate a trigger glow discharge at trigger electrodes 57 at one end of the envelope 30 and which are connected to the secondary of a transformer 58 whose primary receives the input pulse 56.

The operation of the arrangement of FIG. 4 is substantially identical to that described in connection with FIG. 2 except that following the first scan the input pulse establishing a trigger glow discharge at the trigger electrodes 57 also operates the switching amplifier to switch the polarity of the bias potential from negative to positive or vice versa depending on the previous polarity. Thus, any metal transferred from one electrode to the other during the first scan is returned to its original electrode during the next scan and the only electrode loss is that small proportion of metal which vaporizes to the walls of the tube.

It will be noted that with the arrangement of FIG. 4 it is no longer necessary to provide leaking resistances for the capacitors 38. As each is charged during one scan, it retains its charge throughout the entire scan but when the polarity of the bias potential is reversed, the capacitors are now charged in a direction aiding the enabling of the gaps. Thus the capacitors may be smaller than in the arrangement of FIG. 2 because of the fact that on subsequent scans the capacitors are charged in a negative sense with respect to the applied voltage.

In the arrangement of FIG. 4, the phase of the clocking transfer potentials applied to the scan transfer lines 40, 42 must be shifted when the supply voltage polarity V is changed. That is to say, when the supply voltage polarity is positive, the transfer line 40 must initially be positive. This is accomplished with the positive bias voltage being greater in magnitude than the alternate negative bias voltage by an amount equal to the amplitude of the positive transfer pulse from sources 44, 46 to be supplied alternately to the lines 40, 42.

The arrangement shown in FIG. 5 is similar to the arrangement of FIG. 2 except that in lieu of a common electrode the first electrode means comprises two sets of alternately connected electrodes 60, 62 with all the electrodes 60 of one set being connected to a common bus 64 and all the electrodes 62 of the other set being connected to a second common bus 66. The buses 64, 66 are connected through respective alternating potential sources of opposite phase 68, 70 to one terminal of a bias potential source 72. The other terminal of the source 72 is connected in common through capacitors 74 to electrodes 76 spaced from the respective electrodes 60, 62 to define glow discharge gaps. As in FIG. 2, leakage resistors 78 bridge the capacitor 74 and at one end of the tube 80 containing the electrodes are trigger electrodes 82.

The sources 68, 70 effect switching of the glow discharge by increasing and decreasing in phased sequence the voltage level supplied to the buses 64, 66 and as before, the capacitors prevent reverse scanning. Stated differently, the potentials of the sources modify the bias potentials supplied to the respective buses 64, 66 upwardly and downwardly in precisely timed sequence to insure the scanning of the tube at a controlled rate so that the rate of scan is controlled by the frequency of the alternating potential sources.

It can be seen from the above that the invention, while not limited to the examples shown and described, provides scanner means which are superior to those of the prior art in that the scanning rate is maintained and established by multiphase, clocking transfer potential so that the transfer of the glow discharge from gap to gap takes place at a precisely controlled time period. Also, the invention discloses the use of alternating polarity for the bias potential to render at least twice the life and usually much greater than this to the electrodes through the ability to transfer back and forth between these electrodes any sputtered conductive material. Furthermore, not only does the reverse polarity prolong electrode life but it substantially simplifies construction by eliminating the need for shunting resistances across each of the capacitors.

The scanning tubes shown and described has application in addressing memories, scanning X-Y or other type of matrix of an electroluminescent panel for information displays and television, for multiplexing and providing a signal at the required coordinates as in a strip chart or an X-Y recorder.

What is claimed is:

l. A scanning system comprising first and second sets of individual side-by-side electrodes, the electrodes of one set being arranged in spaced opposition to electrodes of the second set to define a longitudinally extended row of glow discharge gaps, a common envelope containing an ionizable medium enclosing said electrodes, a source of potential connected to the electrodes of said first set, a capacitor connected between said source and each electrode of said first set, first means electrically interconnecting alternate electrodes of the second set, second means electrically interconnecting the electrodes intervening between said alternate electrodes, means for applying a biassing potential to the first and second electrode interconnecting means, and first and second pulsating transfer voltage signal sources of opposite phases connected respectively to said first and second electrical interconnecting means, said sources modifying the bias potential on said second set of electrodes to initiate and extinguish glow discharges at said gaps at a rate determined by the frequency of pulsations of said sources of transfer voltage signal.

2. A scanning system comprising first and second longitudinally extending electrode means, at least one of the electrode means being a series of side-by-side individual electrodes spaced from the other electrode means to define a series of aligned, longitudinally extending glow discharge gaps, a common envelope containing an ionizable medium enclosing said electrodes, means for applying a bias potential to one only of said electrode means, first means electrically interconnecting alternate gaps and second means electrically interconnecting the gaps intervening between alternate gaps, a capacitor connected between said first and second electrical interconnecting means and each of the respective gaps, first and second pulsating transfer voltage signal sources of opposite phases connected to said first and second electrical connecting means, trigger electrodes at one end of the line of gaps, means for applying a high voltage pulse to said trigger electrodes to establish therebetween a trigger glow discharge, pulse responsive switch means for reversing polarity of said first and second electrode means, and means connecting said switch means to said means for applying a high voltage pulse to said trigger electrodes to effect reversal of the polarity of said electrode means simultaneously with the production of a trigger glow discharge at said trigger electrode. 

1. A scanning system comprising first and second sets of individual side-by-side electrodes, the electrodes of one set being arranged in spaced opposition to electrodes of the second set to define a longitudinally extended row of glow discharge gaps, a common envelope containing an ionizable medium enclosing said electrodes, a source of potential connected to the electrodes of said first set, a capacitor connected between said source and each electrode of said first set, first means electrically interconnecting alternate electrodes of the second set, second means electrically interconnecting the electrodes intervening between said alternate electrodes, means for applying a biassing potential to the first and second electrode interconnecting means, and first and second pulsating transfer voltage signal sources of opposite phases connected respectively to said first and second electrical interconnecting means, said sources modifying the bias potential on said second set of electrodes to initiate and extinguish glow discharges at said gaps at a rate determined by the frequency of pulsations of said sources of transfer voltage signal.
 2. A scanning system comprising first and second longitudinally extending electrode means, at least one of the electrode means being a series of side-by-side individual electrodes spaced from the other electrode means to define a series of aligned, longitudinally extending glow discharge gaps, a common envelope containing an ionizable medium enclosing said electrodes, means for applying a bias potential to one only of said electrode means, first means electrically interconnecting alternate gaps and second means electrically interconnecting the gaps intervening between alternate gaps, a capacitor connected between said first and second electrical interconnecting means and each of the respective gaps, first and second pulsating transfer voltage signal sources of opposite phases connected to said first and second electrical connecting means, trigger electrodes at one end of the line of gaps, means for applying a high voltage pulse to said trigger electrodes to establish therebetween a trigger glow discharge, pulse responsive switch means for reversing polarity of said first and second electrode means, and means connecting said switch means to said means for applying a high voltage pulse to said trigger electrodes to effect reversal of the polarity of said electrode means simultaneously with the production of a trigger glow discharge at said trigger electrode. 